If a heart valve is found to be malfunctioning because it is defective or diseased, minimally invasive methods are known for repair and replacement of the heart valve. Transcatheter Valve Therapies (TVT) include procedures referred to as Transcatheter Aortic Valve Implantation (TAVI) and Transcatheter Mitral Valve Implantation (TMVI).
TVT provides methods for replacing diseased valves which avoid the need for open heart surgery. Procedures such as TAVI have been developed over the last decade and have become more common procedures in recent years. While there have been many recent advances in systems and apparatus for TVT and for related diagnostic procedures, interventional cardiologists who perform these procedures have identified the need for improved apparatus for use in TVT, such as, heart valve replacement. They are also seeking improved diagnostic equipment that provides direct measurements of important hemodynamic cardiovascular parameters before, during and after TVT.
The above referenced related PCT application no. PCT/IB2012/055893 (Publication no. WO/2013/061281), having common inventorship and ownership with the present application, discloses a multisensor micro-catheter or guidewire which comprises a distal end portion containing multiple optical sensors arranged for measuring blood pressure at several sensor locations simultaneously in real-time, and optionally also blood flow. In particular, the multisensor micro-catheter or guidewire is designed for use in minimally invasive surgical procedures for measurement of intra-vascular pressure gradients, and in particular, for direct measurement of a transvalvular pressure gradient within the heart.
To obtain accurate measurements of hemodynamic parameters such as blood pressure, blood flow, a blood pressure gradient, or other parameters within the heart, it is desirable that the sensor guidewire does not interfere with normal operation of the heart and the heart valves. Thus, beneficially, a fine diameter guidewire, e.g. ≤0.89 mm diameter, with a flexible tip, facilitates insertion through a heart valve without trauma, and reduces interference with valve operation. That is, when the sensor guidewire is inserted through the valve, it preferably causes minimal interference with the movement of the valve and/or does not significantly perturb the transvalvular pressure gradient or other parameters. For example, in use, a multisensor guidewire may be introduced via the aorta, through the aortic valve, and positioned so that the optical pressure sensors are located both upstream and downstream of the aortic valve, for direct measurement of the transvalvular blood pressure gradient, and optionally also blood flow, with minimal disruption of the normal operation of the aortic valve. Accordingly, a fine gauge guidewire minimizes disruption of the heart valve activity during measurement, to obtain accurate measurements of the transvalvular pressure gradient or other parameters.
A reliable measurement of a transvalvular pressure gradient through several cardiac cycles is an important parameter to assess whether the heart valve is functioning well or malfunctioning. An optical multisensor pressure sensing guidewire of this structure provides a valuable tool that an interventional cardiologist can use to facilitate direct measurements of cardiovascular parameters, including a transvalvular pressure gradient. Such measurements provide information relating to parameters, such as, an aortic regurgitation index, stenotic valve orifice area and cardiac output.
As described in the above referenced related patent applications, typically, a support guidewire used for TVT comprises an outer layer in the form of a flexible metal coil, and a central metal core wire or mandrel. The outer metal coil and inner core wire act together to provide a suitable combination of flexibility and stiffness, which, together with a suitably shaped tip, allow the guidewire to be directed or guided through the blood vessels into the heart. In the multisensor guidewire disclosed in the above referenced PCT International Application no. PCT/IB2012/055893, the optical sensors, e.g. 3 or 4 optical pressure sensors are located in a distal end portion of the sensor guidewire, and coupled by respective individual optical fibers to an optical input/output at the proximal end of the guidewire. It will be appreciated that to fit a plurality of optical sensors and optical fibers within a guidewire comprising a small gauge (≤0.89 mm) outer coil, the diameter of core wire is made as small as possible, i.e. to allow sufficient space around the core wire to accommodate the optical fibers and sensors. However, use of a smaller diameter core wire significantly reduces the stiffness of the multisensor guidewire. That is, the optical fibers and sensors take up space within the micro-catheter or guidewire coil but do not contribute significantly to the stiffness.
In testing of prototype multisensor guidewires, it has been found that the strong blood flow and turbulence within the heart can be sufficient to displace a small-gauge flexible guidewire, and tends to push the guidewire back into the aorta. Thus, during measurement of a transvalvular pressure gradient, movement of the guidewire may create difficulty in positioning the sensors and the cardiologist may need to readjust the positioning of the guidewire to maintain the pressure sensors each side of the heart valve. On the other hand, in a multisensor guidewire of this structure, to accommodate a plurality of optical sensors and respective optical fibers around a larger diameter stiffer core wire would require a larger outside diameter outer coil, i.e. larger than 0.89 mm. While a larger gauge, stiffer guidewire would be less easily displaced during measurements, for measurement of transvalvular pressure gradients, it would tend to interfere more with normal heart valve operation, and may increase the risk of tissue damage. Accordingly, a need for further improvements has been identified.
If diagnostic measurements of hemodynamic/cardiac parameters indicate the need for valve replacement, minimally invasive TVT procedures, such as TAVI, can be performed to insert a replacement or prosthetic valve, e.g. comprising leaflets made of biologic tissue supported within an expandable metal frame.
Examples of current prosthetic valves and valve delivery systems are illustrated and described and illustrated in an article entitled “Current Status of Transcatheter Aortic Valve Replacement”, by John G. Webb, MD, David A. Wood, M, Vancouver, British Columbia, Canada; Journal of the American College of Cardiology, Vol. 60, No. 6, 2012.
Very briefly, the procedure requires that a support guidewire, which is relatively stiff guidewire (TAVI guidewire) with a flexible tip, is introduced into the heart and through the aortic valve. For example, the interventional cardiologist introduces the support guidewire through a catheter inserted into the femoral artery, i.e. in the groin, and moves it up through the aorta into the heart. The tip of the TAVI guidewire is introduced into the aorta, through the malfunctioning aortic valve, and into the left ventricle of the heart. Once the support guidewire is anchored within the ventricle, a delivery device holding the replacement valve is passed over the support guidewire. The cardiologist guides the delivery device carrying the replacement valve over the support guidewire and manoeuvres the valve into position within the aortic valve. The replacement valve is expanded, so that the patient's malfunctioning aortic valve is pushed out of the way. The valve frame may be self-expandable or balloon-expandable, depending on the valve type and the delivery system. Once expanded, the metal frame engages the wall of the aorta and holds the replacement valve in position. When the delivery system is withdrawn, the leaflets on the replacement valve are able to unfold and then function in a manner similar to the leaflets of the natural aortic valve.
Commercial availability of an optical multisensor guidewire as described in the above referenced co-pending patent application would provide the interventional cardiologist with a useful tool for directly measuring a pressure gradient before and after such a procedure for valve repair or replacement, e.g. for TAVI. For example, it is envisaged that the interventional cardiologist would introduce the fine gauge multisensor guidewire to measure a transvalvular pressure gradient, and optionally blood flow, to assess pre-implantation functioning of the heart and the damaged or malfunctioning aortic valve. After withdrawing the multisensor guidewire, the cardiologist would perform a transcatheter heart aortic valve implantation procedure using a specialized, more robust and stiffer, support guidewire (TAVI guidewire) to deliver the valve implant into the heart and perform the implantation. Subsequently after completing the TAVI procedure the TAVI guidewire would be withdrawn. The multisensor guidewire would then be reintroduced to measure a transvalvular pressure gradient and flow, to assess post-implant functioning of the replacement valve.
For TAVI, a relatively stiff support guidewire, typically 0.035 inch or 0.89 mm in diameter, is required. For example, guidewire manufacturers may use a descriptive term, such as, “stiff” or “super stiff” to provide an indication of the guidewire stiffness. Based on experience, an interventional cardiologist will select a guidewire with an appropriate stiffness and/or other mechanical characteristics to suit a particular TVT procedure. Such a description of stiffness or flexibility can be related in mechanics to a measurement of a flexural modulus, which is a ratio of stress to strain in flexural deformation, or, what may be described as the tendency for a material to bend.
During a TAVI procedure, the support guidewire must be firmly anchored within the left ventricle so that the replacement valve can be accurately positioned and held firmly in place while it is expanded. When such a guidewire is introduced into the left ventricle of the heart through the aortic valve, if too much force is applied to the guidewire or it is pushed too far, there is some risk that the guidewire could cause damage or trauma to the heart tissues, e.g. damage to the aortic wall or ventricular perforation and pericardial effusion resulting in pericardial tamponade. Moreover, there is increased risk of trauma or damage to the heart wall in a diseased, weakened or calcified heart. To reduce risk of trauma or ventricular perforation, typically the tip of the support guidewire is relative soft and flexible. It may be pre-formed as a J-tip or it may be resiliently deformable so that it can be manually shaped as required by the cardiologist. Recently, specialized TAVI guidewires have become commercially available with pre-formed curved tips of other forms. For example, the Boston Scientific Safari™ pre-shaped TAVI guidewire has a double curve tip, and the Medtronic Confida™ Brecker Curve™ guidewire has a spiral tip. Reference is also made, by way of example, to structures described in US patent publication no. US2012/0016342 and PCT Publication no. WO2010/092347, each to Brecker, entitled “Percutaneous Guidewire”; PCT Publication no. WO2014/081942, to Mathews et al., entitled “Preformed Guidewire”; and PCT Publication no. 2004/018031 to Cook, entitled “Guidewire”. See also, an article by D. A. Roy et al., entitled “First-in-man assessment of a dedicated guidewire for transcatheter aortic valve implantation”, EuroIntervention 2013; 8, pp. 1019-1025.
While significant advances have recently been made, interventional cardiologists have identified a need for further improvements or alternatives to available guidewires and diagnostic tools for use in minimally invasive cardiac procedures, such as TAVI, or other TVT. In particular, it is desirable to have improved apparatus to simplify or facilitate TVT procedures, including apparatus that will assist in reducing the risk of tissue trauma, e.g. damage to the aorta, the valve or the ventricular wall when much force is exerted on the support guidewire. Additionally, improved systems and apparatus that would provide for direct (in situ) diagnostic measurements before and after TVT procedures would potentially assist in understanding factors that contribute to successful outcomes and/or issues that may contribute to mortality or need for re-intervention.
Thus, an object of the present invention is to provide for improvements or alternatives to known cardiovascular support guidewires for TVT and/or to multisensor guidewires for that enable direct measurements of cardiovascular parameters, such as a transvalvular pressure gradient.